Electronic lock with inductively coupled tuned key card



Get. 3, 1967 ELECTRONIC LOG Filed May 2, 1966 c. F BURNEY 3,344,629

K WITH INDUCTIVELY COUPLED TUNED KEY CARD 5 Sheets-Sheet l lIE-1 L I: m W '2 'l INVENTOR.

CHARLES F. BURNEY IE- Z.

AI IORNEY C. F. BURNEY Oct. 3, 1967 ELECTRONIC LOCK WITH INDUCTIVELY COUPLED TUNED KEY CARD 5 Sheets-Sheet 2 TUNED FILTER.

Filed May 2, 1966 AMPLIFIER OSCILLATOR I V MIXER w 3 M h\ R U V A C L R All C 8 9 2 2/ U Ic 0 R 3 L m 3 R O T A L L C S O INVENTOR.

CHARLES F. BURNEY ATTORNEY Oct. 3, 1967 c. F BURNEY 3,344,629

ELECTRONIC LOCK WITH INDUCTIVELY COUPLED TUNED KEY CARD Filed May 2, 1966 5 Sheets-Sheet 3 INVENTOR.

CHARLES E BURNEY BY 9% W ATTORNEY United States Patent 3,344,629 ELECTRGNIC LOCK WITH INDUCTIVELY COUPLED TUNED KEY CARD Charles F. Burney, Milpitas, Calih, assignor to Sylvama Electric Products Inc., a corporation of Delaware Filed May 2, 1966, Ser. No. 547,020 3 Claims. (Cl. 7tl28tl) ABSTRACT OF THE DISCLOSURE A door lock is opened by a printed circuit pass card when inserted in a slot to inductively couple the output of one of two oscillators and the input to a mixer. A narrow passband filter at the output of the mixer discriminates against all frequencies except that produced by a valid pass card. An alarm circuit energized through a switch closable by the card in the key slot is disabled only by the filter output, thus providing an alarm if an invalid card is used. Printed inductors and capacitors on the card are so arranged that the tuning characteristic of the card is selectively changeable by punching the card.

This invention delates to an improved electronic locking system.

A lock system generally comprises a portable coded key and a lock actuator programmed to function when the key is inserted into it. In an electronic locking system, the inserted key, which may take the form of a card, affects the operation of an electrical circuit so as to actuate the lock mechanism. An example of the latter is the system described in Patent No. 2,779,874 in which the key card forms part of a multielement capacitor in the circuit. The inherently critical spacing between capacitor plates imposes severe limitations on positioning of the card in the slot. Also, reduction of the physical size of the key card for convenience of the user is limited by the necessity of providing the required capacitor plate area to operate the system in several coded modes.

An object of this invention is the provision of a highly selective electronic locking system capable of effectively discriminating against spurious signals or conditions that may tend to open the lock.

A further object is the provision of a locking system operated by a wallet-size key card that is readily programmable for one of a large number of key combinations and yet is extremely diflicult to duplicate.

A further object is the provision of such a system which is operated by an easily insertable key card with a minimum wear on the parts.

Still another object is the provision of a lock system having a conveniently small printed circuit key with a capacity for a large number of easily programmable code combinations.

A more specific object is the provision of a frequencycoded electronic lock system.

A further object is the provision of a locking system which responds with an alarm to an attempt to defeat the system.

These and other objects of the invention are accomplished with a locking system in which a coded radio frequency (RF) signal is mixed with a reference RF signal and the output is monitored to either actuate the lock or an alarm. The frequency of one of the two signals from the RF sources is determined by a tuned circuit, preferably printed on a key card and inductively coupled into the system when inserted into the key slot of the locking system. The key card is opaque to hide the tuned circuit thereon which has interconnected capacitance and inductance 3,344,629 Patented Oct. 3, 1967 elements with values selectively predetermined as by external or internal punching of the card. The lock mechanism may be preset to one of many different code combinations by change of the inductance or the capacitance (or both) on the card, by adjustment of frequency generators and monitor, or by a combination of these changes. The inductance coils on the card connect to the tuned circuit and are positioned to effect inductive coupling of the card circuit to the fixed circuit of the system.

Other objects of the invention become apparent from the following description of a preferred embodiment thereof reference being had to the accompanying drawings in which:

FIGURE 1 is a schematic representation of a person seeking admittance through a doorway protected by a looking system of the type embodying this invention;

FIGURE 2 is a greatly enlarged view of part of FIG- URE 1 with a wall broken away to show the position of the parts of the locking system;

FIGURE 3 is a block diagram of the circuits comprising the locking system;

FIGURES 4 and 5 are schematic diagrams of oscillators and key card circuits which may be utilized in the practice of the invention;

FIGURE 6 is a plan view of a key card with the opaque or circuit obscuring substance removed to show the printed configuration; and

FIGURE 7 is a section taken on line 7-7 of FIG- URE 6.

Referring now to the drawings, an embodiment of the invention is shown in FIGURES 1 and 2 in conjunction with a door 11 which is locked and unlocked by a re tractable bolt 11 adapted to project into the side of the door. Bolt 11 is moved between locking and unlocking positions by actuator 12, such as a solenoid which is enengized in a manner described below when a key card 13 is inserted in a slot 14 of the mechanism 15 mounted next to the door. Such a locking system is especially useful to control access to classified areas, private clubs, and the like, but it should be understood that these are merely a few of many examples of the way in which the invention may be practiced.

A schematic block diagram of a preferred embodiment of the invention is shown in FIGURE 3 and comprises an RF oscillator 16 having an output with a frequency connected to a mixer 17. Frequency f of oscillator 16 may be selected by connection of one of a bank of crystals 18 to the rest of the oscillator circuit by a switch 19. A second input to mixer 17 has a frequency f and is provided by another RF oscillator 20 having a frequency-determining circuit which includes a tuned circuit 21 wholly contained within card 13 and inductively coupled to the mixer. Thus, the frequency of RF energy generated by oscillator 20 is determined by the parameters of tuned circuit 21 which therefore controls the frequency f of second input to mixer 17.

The output of mixer 17 contains, inter alia, a signal having a frequency f equal to the difference of the input frequencies to the mixer and is fed through a tuned filter 22. having a narrow bandpass characteristic set to pass only the difference frequency output from mixer 17 produced by a valid key card 13.

The output of filter 22 passes to an amplifier 24 and is connected by line 28 to lock actuating circuit 12 and also by line 29 to alarm circuit 30. An output signal on line 28 energizes lock circuit 12 to cause bolt 11 to be withdrawn from the door for unlocking it.

Alarm circuit 30 is connected by line 31 to a source S of power through a normally open switch 33 which preferably is so located in slot 14 of lock mechanism 15 that card 13 must be fully inserted in the slot to close the switch. When switch 33 is closed, alarm circuit 30 is preconditioned so as to be ready to give an alarm. If a signal, called an inhibit signal, is applied to the alarm circuit from amplifier 24 via line 29, the circuit 30 is not activated and no alarm is given. On the other hand, if no output comes from the amplifier, the alarm circuit is not disabled and the signal on line 31 produces an-alarrn. Switch 33 also serves to connect power source S to other elements of the circuit which are therefore preferably normally deenergized except when an attempt is made to open the lock.

Card 13 has a self-contained tuned circuit comprising aparallel-connected inductor 35 and capacitor 36 together with inductive coupling coils 37 and 38 which couple the card circuit to oscillator output coil 39 and mixer input coil 40, respectively.

There are two codable subsystems in this locking systern, the card 13 and the frequency components comprising oscillators 16 and 20 and tuned filter 22. The whole locking system may be programmed through selection of the characteristics of either subsystem or both. For example, the frequency of oscillator 16 might be determined by selection of a particular crystal via switch 19 and filter 22 thereafter adjusted to ass the particular frequency i produced by mixing of frequency h with frequency f from a valid key card circuit. Alternatively, the input frequency f to the mixer might be changed by adjustment of oscillator 20 or by changing the parameters of the tuned circuit on the card as will be explained in greater detail below in conjunction with the description of the card circuit shown in FIGURE 6. The permutations and combinations of these several variables provide an extremely large number of potential codes which are readily and conveniently established by simple tuning procedures.

The locking system is programmed to respond to a key card 13 having a tuned circuit with predetermined parameters by selection of an operating frequency for oscillator 16 with crystal selector switch 19, adjustment of the frequency of oscillator 20, and by adjustment of the bandpass of filter 22, preferably by tuning of the filter. All circuits of the system are normally deenergized, being disconnected from the power source by normally open switch 33. In order to open the locked door, card 13-is inserted into slot 14 until it bottoms against switch 33 to close it and energize the circuits. The width and height of slot 14 is slightly greater than the width and thickness, respectively, of card 13 so that the latter may be freely guided into the slot without obstruction and yet is in proper position when bottomed therein so that card coupling coils 37 and 38 are in full energy transfer relationship with coils 39 and 44 respectively.

The tuned circuit of card 13 becomes a part of the oscillator 20 so that the frequency f of the signal on mixer input coil 40 is dependent on the parameters of the card circuit. The input signal to the mixer from oscillator 16 and the signal on coil 40 are mixed or heterodyned in mixer 17 and produce a signal at the mixer output with a frequency A equal to the difference between f and f The pass band of filter 22 is selected to move pass signals having a frequency f to amplifier 24. All other frequencies are rejected by filter 22 and therefore produce no output from the filter.

The signal passed by filter 22 produces an output from amplifier 24 to line 28 which energizes a lock circuit 12 to withdraw bolt 11 from the door. Alarm circuit 30 is also conditioned by input on line 31 from power source S to give an alarm but is prevented from doing so by the inhibit signal from amplifier 24 on line 29.

In the event an invalid card or other device is inserted in slot 14 sufiiciently to depress and close switch 33, the output of mixer 17 is such that no output is produced by amplifier 24 either to energize the unlocking circuit 12 or to prevent circuit 30 from giving an alarm. Thus, an at tempt to defeat the system is immediately identified to facilitate corrective action and to discourage further tampering.

Various types of RF oscillators 20 may be utilized in practice of this invention. Similarly, the inductive coupling of energy from oscillator 20 into the tuned circuit 21 of key card 13 may be accomplished in different ways, as long as the card circuit forms a part of the circuit which determines the output frequency of oscillator 20. By way of example, oscillator 20' shown in FIGURE 4 may comprise a transistor 41 with a tank circuit 42 having an inductance 43 which is coupled both to input coupling 37' of card 13' and to feedback coil 44 of the transistor. Alternatively, oscillator 20" shown in FIGURE 5 comprises a transistor 47 with emitter and collector inductively coupled together and to the resonant circuit of card 13 by coil 37" on the card.

In accordance with the invention, key card 13 comprises a layer of synthetic material 45, see FIGURE 6 and 7, which is pervious to RF energy and on which the tuning circuit 21 preferably is printed by well-known printed circuit techniques. The circuit is generally rectangularly configured with loops 46 and 47 comprising the input and output coupling coils located at the top corners, as viewed, and connected in series with each other and in parallel with a group 48 of line capacitors and with a bank 49 of inductance loops. The capacitor group consists of a plurality of closely spaced parallel lines, of which alternate lines 4802 are connected to trunk 50- by a common connection 51 and the remaining parallel lines 48b are connected to trunk 52 by line connections 53a. Also, lines 48]) are grouped in successive pairs with the lines of each pair connected together by a line connection 53b. The bank of inductors comprise individual rectangular loops 55 formed in electrical series with each other and connected in parallel with a cross trunk 56 by connections 57. Trunks 5t), 52, and 56 are connected in series. Both sides of layer 45 may be covered by opaque, RF pervious layers 59 and 60 permanently bonded thereto, and which not only hide the circuit 21 but also provide a means for carrying appropriate legends, titles, or other messages useful to the purpose of the card. Alternatively, the card may comprise two layers of opaque material sandwiched together and permanently sealed with the tuned circuit on the inside.

In the form shown in FIGURE 6, circuit 21 has maximum capacitance since all plates (lines) of the capacitors are connected to the trunks 50 and 52. The circuit has minimum inductance since all of the loops 55 are short-circuited by cross trunk 56. In accordance with the requirements of the application, the magnitudes of inductance and capacitance of circuit 21 may be initially programmed and thereafter changed, as desired, by a simple external punching operation which selectively breaks one or more electrical connection at the capacitor and at the inductance loops. More specifically, capacitance may be decreased from a maximum in steps by punching the card so as to successively sever connections 53b, thereby removing one plate 48b with each such severing operation, or to cut connections 53a separately so as to remove a pair of plates 48b with each such operation. Conversely, trunk 56, which short-circuits all of the inductance loops, may be successively cut by punching to increase the magnitude of inductance in the circuit from a minimum. Thus, each segment of trunk 56 between adjacent loop connections 57 may be selectively severed to connect the included inductance loop into the circuit. The permutations and combinations of codes available by such card punching are significantly large and yet the compactness of the circuit is conveniently adaptable to cards of wallet size or smaller.

It should be noted that the location of the punched holes does not necessarily indicate the magnitude of the capacitance or inductance in the circuit even with identically configured capacitor plates and inductance loops;

that is, one inductance is added to the circuit irrespective of which segment of trunk 26 is severed, and similarly a unit of capacitance is removed from the circuit for each punching of a connection 53a or 5317. Dummy holes may also be punched in a card to further disguise the card and enhance the security of the system.

Changes, modifications, and improvements to the above-described embodiment of the invention may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, the circuit 21 on card 13 may initially be formed with predetermined inductance and capacitance values to give a coded frequency, and thus no external punch marks would appear on the card. Also, the card circuit may be formed by other than printed circuit techniques. The claims define essential features of novelty in the invention.

I claim:

1. A key card for an electronic locking system comprising an electromagnetic wave-pervious electrically nonconducting sheet having a circuit formed thereon and covered by another like sheet,

said circuit comprising a pair of inductive coupling coils connected in series,

a plurality of parallel line capacitor elements separately connected in parallel with said coils whereby a unit of capacitance is removed from said circuit for each of said connections that is severed, and

a plurality of series-connected inductance elements separately shunt-connected across said coupling coils whereby a unit of inductance is added to said circuit for each of said shunt connections that is severed.

2. A system for operating a lock comprising a source of power,

electromagnetic wave generator means adapted to produce a signal having a predetermined frequency,

said generator means. comprising fixed circuits and a key card having a selfcontained frequency control circuit selectively positionable in an operative location adjacent to said fixed circuits to produce said predetermined frequency,

a normally open switch electrically connected between said power source and said fixed circuits and closable by the card in said operative location,

a filter responsive only to said signal for producing an output,

a utilization circuit responsive to the output of said filter for changing the operating state of the lock, and

an alarm circuit having one input connected to said power source through said switch and a second input responsive to the output of said filter for disabling the alarm circuit.

3. A system for operating a lock comprising electromagnetic wave generator means adapted to produce a signal having a predetermined frequency,

said generator means comprising fixed circuits and a key card having a self-contained frequency control circuit selectively positionable in an operative location adjacent to said fixed circuits to produce said predetermined frequency, said generator means comprising first and second oscillators having outputs with different frequencies, one of said oscillators including the circuit on said key card, and means for mixing the output of said oscillators to produce said signal, said card circuit comprising interconnected inductance and capacitance elements and coupling loops for inductively coupling said elements to one of the oscillators and to the mixing means,

a fiilter responsive only to said signal for producing an output, and

a utilization circuit responsive to the output of said filter for changing the operating state of the lock.

References Cited UNITED STATES PATENTS 2,541,461 2/ 1951 Churchill 340-274 2,774,060 12/ 1956 Thompson 340-258 2,816,229 12/ 1957 Vantine 33140 2,921,152 1/1960 Sim Jian 340-274 3,093,994 6/1963 Richard 317-134 3,136,307 6/1964 Richard 340-274 ROY LAKE, Primary Examiner.

JOHN KOMINSKI, Examiner. 

1. A KEY CARD FOR AN ELECTRONIC LOCKING SYSTEM COMPRISING AN ELECTROMAGNETIC WAVE-PERVIOUS ELECTRICALLY NONCONDUCTING SHEET HAVING A CIRCUIT FORMED THEREON AND COVERED BY ANOTHER LIKE SHEET, SAID CIRCUIT COMPRISING A PAIR OF INDUCTIVE COUPLING COILS CONNECTED IN SERIES, A PLURALITY OF PARALLEL LINE CAPACITOR ELEMENTS SEPARATELY CONNECTED IN PARALLEL WITH SAID COILS WHEREBY A UNIT OF CAPACITANCE IS REMOVED FROM 